/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package javax.servlet;

/**
 * Defines an exception that a servlet or filter throws to indicate that it is
 * permanently or temporarily unavailable.
 * <p>
 * When a servlet or filter is permanently unavailable, something is wrong with
 * it, and it cannot handle requests until some action is taken. For example, a
 * servlet might be configured incorrectly, or a filter's state may be
 * corrupted. The component should log both the error and the corrective action
 * that is needed.
 * <p>
 * A servlet or filter is temporarily unavailable if it cannot handle requests
 * momentarily due to some system-wide problem. For example, a third-tier server
 * might not be accessible, or there may be insufficient memory or disk storage
 * to handle requests. A system administrator may need to take corrective
 * action.
 * <p>
 * Servlet containers can safely treat both types of unavailable exceptions in
 * the same way. However, treating temporary unavailability effectively makes
 * the servlet container more robust. Specifically, the servlet container might
 * block requests to the servlet or filter for a period of time suggested by the
 * exception, rather than rejecting them until the servlet container restarts.
 *
 * @author Various
 */
public class UnavailableException extends ServletException {

	private static final long serialVersionUID = 1L;

	private final Servlet servlet; // what's unavailable
	private final boolean permanent; // needs admin action?
	private final int seconds; // unavailability estimate

	/**
	 * @param servlet the <code>Servlet</code> instance that is unavailable
	 * @param msg     a <code>String</code> specifying the descriptive message
	 * @deprecated As of Java Servlet API 2.2, use
	 * {@link #UnavailableException(String)} instead.
	 */
	@SuppressWarnings("dep-ann")
	// Spec API does not use @Deprecated
	public UnavailableException(Servlet servlet, String msg) {
		super(msg);
		this.servlet = servlet;
		permanent = true;
		this.seconds = 0;
	}

	/**
	 * @param seconds an integer specifying the number of seconds the servlet
	 *                expects to be unavailable; if zero or negative, indicates that
	 *                the servlet can't make an estimate
	 * @param servlet the <code>Servlet</code> that is unavailable
	 * @param msg     a <code>String</code> specifying the descriptive message,
	 *                which can be written to a log file or displayed for the user.
	 * @deprecated As of Java Servlet API 2.2, use
	 * {@link #UnavailableException(String, int)} instead.
	 */
	@SuppressWarnings("dep-ann")
	// Spec API does not use @Deprecated
	public UnavailableException(int seconds, Servlet servlet, String msg) {
		super(msg);
		this.servlet = servlet;
		if (seconds <= 0)
			this.seconds = -1;
		else
			this.seconds = seconds;
		permanent = false;
	}

	/**
	 * Constructs a new exception with a descriptive message indicating that the
	 * servlet is permanently unavailable.
	 *
	 * @param msg a <code>String</code> specifying the descriptive message
	 */
	public UnavailableException(String msg) {
		super(msg);
		seconds = 0;
		servlet = null;
		permanent = true;
	}

	/**
	 * Constructs a new exception with a descriptive message indicating that the
	 * servlet is temporarily unavailable and giving an estimate of how long it
	 * will be unavailable.
	 * <p>
	 * In some cases, the servlet cannot make an estimate. For example, the
	 * servlet might know that a server it needs is not running, but not be able
	 * to report how long it will take to be restored to functionality. This can
	 * be indicated with a negative or zero value for the <code>seconds</code>
	 * argument.
	 *
	 * @param msg     a <code>String</code> specifying the descriptive message,
	 *                which can be written to a log file or displayed for the user.
	 * @param seconds an integer specifying the number of seconds the servlet
	 *                expects to be unavailable; if zero or negative, indicates that
	 *                the servlet can't make an estimate
	 */
	public UnavailableException(String msg, int seconds) {
		super(msg);

		if (seconds <= 0)
			this.seconds = -1;
		else
			this.seconds = seconds;
		servlet = null;
		permanent = false;
	}

	/**
	 * Returns a <code>boolean</code> indicating whether the servlet is
	 * permanently unavailable. If so, something is wrong with the servlet, and
	 * the system administrator must take some corrective action.
	 *
	 * @return <code>true</code> if the servlet is permanently unavailable;
	 * <code>false</code> if the servlet is available or temporarily
	 * unavailable
	 */
	public boolean isPermanent() {
		return permanent;
	}

	/**
	 * Returns the servlet that is reporting its unavailability.
	 *
	 * @return the <code>Servlet</code> object that is throwing the
	 * <code>UnavailableException</code>
	 * @deprecated As of Java Servlet API 2.2, with no replacement.
	 */
	@SuppressWarnings("dep-ann")
	// Spec API does not use @Deprecated
	public Servlet getServlet() {
		return servlet;
	}

	/**
	 * Returns the number of seconds the servlet expects to be temporarily
	 * unavailable.
	 * <p>
	 * If this method returns a negative number, the servlet is permanently
	 * unavailable or cannot provide an estimate of how long it will be
	 * unavailable. No effort is made to correct for the time elapsed since the
	 * exception was first reported.
	 *
	 * @return an integer specifying the number of seconds the servlet will be
	 * temporarily unavailable, or a negative number if the servlet is
	 * permanently unavailable or cannot make an estimate
	 */
	public int getUnavailableSeconds() {
		return permanent ? -1 : seconds;
	}
}
